(a) Field of the Invention
The present invention relates to an additive for a non-aqueous electrolyte which has a low reduction potential and high oxidation stability, a non-aqueous electrolyte comprising the same additive to improve the overall quality of an electrochemical device, and an electrochemical device comprising the same non-aqueous electrolyte.
(b) Description of the Related Art
Recently, as electronic appliances have been downsized and lightened, it has been required to downsize and lighten batteries serving as power sources for the electronic appliances. As a compact, low-weight and high-capacity rechargeable battery, a lithium secondary battery has been commercialized and used widely in portable electronic and communication instruments, such as compact video cameras, portable phones, notebook computers, etc.
A lithium secondary battery comprises a cathode, an anode and an electrolyte. Upon the first charge cycle, lithium ions deintercalated from a cathode active material are intercalated into an anode active material, such as carbon particles, and then are deintercalated again upon discharge. In this way, the battery is rechargeable since the lithium ions serve to transfer energy while reciprocating between both electrodes.
However, as the battery repeats charge/discharge cycles, the cathode active material undergoes a structural collapse, resulting in degradation of the quality of the cathode. Additionally, metal ions dissolved out from the cathode surface upon the structural collapse of the cathode cause electrodeposition onto the anode, resulting in deterioration of the anode. Such degradation of the quality of the battery tends to be accelerated when the cathode potential increases or the battery is exposed to a high temperature.
To solve the above-mentioned problems, a method for adding a material that forms a coating layer on a cathode to protect the cathode to an electrolyte has been suggested (Electrochemical and Solid-State Letters, 7, A462˜465 (2004)). Additionally, it has been suggested that an iodine or bromine compound that forms a complex with a metal ion is used as an additive for preventing deterioration of an anode caused by metal ions dissolved out from the surface of a cathode (Journal of Power Sources, 119-121, 378˜382 (2003)).